Polyurethane foam, which is one of resin components, has been widely used in seat cushions of vehicles, such as automobiles, because of its excellent cushioning characteristics. In particular, cushions having high rebound resilience can provide an ideal body pressure distribution and are very comfortable to sit on. Thus, there is a great demand for such cushions. Seat cushions are required to have moderate hardness, neither too firm nor too soft, and high durability for long-term use with small variations in elasticity, hardness, and thickness.
From the recent perspective of the reduction of load on the environment, there is a demand for plant-derived resins produced from plant resources to take the place of petroleum-derived resins produced from petroleum resources.
Plant-derived resins are produced from raw materials derived from plants, which grow while consuming CO2 in the air by photosynthesis. CO2 emitted into the atmosphere by the combustion of used plant-derived resins therefore does not increase the amount of CO2 in the air. This is called carbon neutrality. Thus, plant-derived resins are receiving attention as materials that contribute to the reduction of load on the environment.
To meet the demand for plant-derived resins, plant-derived castor oil polyols have been used as raw material polyol components in polyurethane foam to reduce environmental load (see, for example, Patent Literatures 1 to 4). However, these foams cannot satisfy the physical properties required by the market, that is, a good balance of moderate hardness and rebound resilience and high durability.
Patent Literature 5 discloses a foam produced from a polyester polyol produced by the condensation of 12-hydroxystearic acid derived from castor oil. However, the foam according to Patent Literature 5 has rebound resilience as low as approximately 50% and cannot provide polyurethane foam having high rebound resilience as a cushioning material for vehicle seat cushions.
Patent Literature 6 discloses a polyurethane foam having a good balance of moderate hardness and rebound resilience and high durability as a cushioning material for vehicle seat cushions. The polyurethane foam is produced from a plant-derived composition for polyurethane foam containing a plant-derived polyol and a low-monool-content polyol in combination.
The polyurethane foam according to Patent Literature 6, however, contains a low amount of plant-derived polyol. Thus, there is still room for improvement in the reduction of load on the environment, as well as improvement in rebound resilience.